Monday, December 10, 2007

G9 and Sunny 16

My first camera, a Kodak Brownie, had no exposure controls. Years later, I had a fully manual camera with exposure controls but no light meter was included or needed. Instead of using a light meter, I simply followed the instructions included with every box of film. These instructions were the recommended camera settings for sunny or cloudy days, light shade, heavy shade, etc. Books and magazines also provided recommended exposures for various indoor and outdoor lighting scenes. Such exposure guides are still valid and useful.

A very useful point of reference for exposure is called the “Sunny 16 Rule”. The rule is that on sunny days where shadows are distinct, a correct exposure is f16 aperture when the shutter speed is set at 1/ISO second. For example, suppose the film (or digital sensor) has an ISO rating of 100. In bright sun, a correct exposure would be f16 at 1/100 second. If the ISO rating were 800, a correct exposure would be f16 at 1/800 second. Of course, given the nature of the f-stops and shutter speeds, there are many other equivalent combinations. For example, the exposures of f16 at 1/100 and f8 at 1/400 provide the same amount of light.

Going back to the Sunny 16 rule, if shadows are not so distinct, f11 might be a better aperture than f16. In deep shade or on overcast days where no shadows are created, f5.6 is recommended.

But the G9 does not have f16! The very nature of small sensor, small focal length cameras such as the G9 (not only the G9!) restrict the use of tiny apertures. Instead, we must adapt the G9 bright sun exposure to the Sunny 16 Rule. Actually, that exposure has already been given: f8 at 1/400 is equivalent to f16 at 100. The G9 does have f8.

I shoot my G9 at ISO 80 when possible. The reference exposure in strong sunlight would be f5.6 at 1/640 second based on the Sunny 16 Rule. However, it seems that f5.6 at 1/500 is often appropriate (even if not theoretically equivalent).

This has been a lot of numbers and there are many combinations but an understanding of the relationships between ISO rating, shutter speed and aperture is an essential part of being a photographer.

Hang on to this post or take notice of the blog labels because this will be used as a point of reference in future posts.

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